MICROSURFACING IN TEXAS

DEPARTMENTAL RESEARCH

STATE DEPARTMENT OF HIGHWAYS AND

PUBLIC TRANSPORTATION

DHT-25.2

DO NOT CIRCULATE

RESEARCH SECTION, FILE DlO-R, P.O. BOX 5051 AUSTIN, TX 78763-5051, 512-465-7403, TexAn 241-7403

TECHNICAL REPORT STANDARD TITLE PAGE

1. Repor. N •• 2. G.Yetfl"' .... Acc ... i ... N •• 3. R.cipi.n'· I C.tol., No.

DHT-25.2

4. Ti.l.ond Subtitl. 5. R.po.t Dot.

"MICROSURFACING IN TEXAS" January, 1991

6. P •• 'o,,,,in, O',onilotion Cod.

7. ' Autho"sl 8. Po,fo'lIIin, O.,oni lo.ion R.port No.

Lisa Lukefahr, Research Engineer Assistant III DHT-25.2

9. Po.fo.",in, Or'OI'Iilo.ion N_. OI'Id Addr... 10. Wort! Unit No. State Department of Highways and Public Transportation Transportation Planning Division, Research Section ~11~.~C~on-t-.o-c-t-o.~G~.-... -t~N~o-.--------------~ P. O. Box 5051 Austin, Texas 78763' 13. T,p. of R.port ond P.ri.d Co" ••• d

~~~~--~--~--~~----------------------------~ 12. Sponlorin, A,onc, N_o .. d Add ....

State Department of Highways and Public Transportation 11th and Brazos Austin, Texas 78701 14. Sponso.in, A,.ncy Cod.

15. Suppl.",ontory Not ••

This is the second in-house report on the usaee of microsurfacing in Texas. Future reports will be conducted on a yearly basis.

16. Aba'roct

Two-thirds of the districts in Texas have used polymer-modified slur'ry seals (also called microsurfacing). Seven of the eight districts that have not yet used this kind of seal will do so at some future time.

The performance of the micro surfacing seal in Texas has generally been promising. The use of this seal to correct rutting and flushing and to improve ride quality and skid resistance has been very good. The availability of materials and equipment for placing slurry seal has improved but is still not ideal. The cost effectiveness of slurry seals older than one year was ranked very high by the districts. The cost of this seal coat has risen 15% within the last year to an average of $1.26 per square yard.

17. K.y Wordl II. Oil""IU"'" Stet_ ....

Microsurfacing, slurry seal, RalUffiac, Seal coat, polymer-modified seal coat

19. Securl.y Clo .. i'. (.f thl •• oport'

Unclassified

Form DOT P 1700.7 , .... ,

m. Security CI ••• lf. (.f thI.,..., Unclassified

21. No. 0' ''''.' 22. Pric.

16

MICROSURFACING IN TEXAS

Prepared by the

Transportation Planning Division (D-lOR)

of the

Texas State Department of Highways

and Public Transportation

* The use of brand or trade names is for informational purposes only

and .does not constitute an endorsement by the Texas State

Department of Highways and Public Transportation.

1

Introduction

A district survey was conducted in November of 1990 to assess the usage of slurry

seals in Texas. Three forms were distributed to each district Form-A (page A-I) was to

be completed by those districts that had never used slurry seals. Form-B (page A-2) was to

be filled out by districts that had completed slurry seals projects within the last twelve

months. Form-C (page A-4) was completed for each existing slurry seal over twelve

months in age. The following report is a brief summary of the findings.

Background

A conventional slurry seal is a mixture of well-graded fme aggregate, mineral filler,

emulsified asphalt and water applied to a pavement as a surface treatment Polymer­

modified slurry seals differ from conventional slurry seals in the following ways:

- a coarser aggregate may be used,

- the slurry seal can be placed in greater thickness, and

- the slurry cures and strengthens faster because of the

polymer-modified asphalt base used in making the emulsion.

The term "microsurfacing" will be used in this report to distinguish polymer­

modified slurry seals from conventional slurry seals.

For additional information about microsurfacing, please refer to the October 1989

issue of the Technical Quarterly (Vol. 5, Issue 2).

Presentation of Survey Results

In 1989, eleven districts reported they had used microsurfacing. In the last year,

the number of districts using this kind of seal has risen to sixteen (Figure 1). Seven of the

eight districts that have not yet used microsurfacing will do so at some time in the future

(four districts have definite plans to use micro surfacing in FY '91).

I

I~~::~:::::J Have Already Used

D Will Use In FY '91

[Z] Will Use In Future

_ Has No Plan To Use

FIGURE 1: DISTRICT USAGE OF MICROSURFACING SEALS

The more widespread use of microsurfacing by districts may indicate that this kind

of seal has gained acceptance for certain types of applications. The most common reason

listed in the survey for applying a new microsurfacing layer was to correct rutting (Figure

2).

50 • Rated Average = 3.84

w 40 0 c( ... z w 30 (,) a: w IlL

0 20

z ~ c(

10 a:

0 1 2 3 4 5

LOW HIGH

FIGURE 2: RUTTING PERFORMANCE

2

The next two most frequent applications were to improve skid resistance and to correct

flushing. The survey results for these categories are shown in Figures 3 and 4. For these

specific applications, 'the results are generally very goOd. Microsurfacing seals were also

successfully used to improve ride quality and to overlay dry pavement.

60 • Rated Average = 4.52

w 50 CJ C

~ 40 w (,) IX

30 w D.

CJ z 20

~ a:

10

0 1 2 345

LOW HIGH

FIGURE 3: SKID RESISTANCE PERFORMANCE

50 • Rated Average = 3.74

w 40 CJ C ... Z w 30 (,) IX W D.

CJ 20 z ~ a: 10

0 1 2 3 4 5

LOW HIGH

FIGURE 4: FLUSHING PERFORMANCE

3

The inability of the microsurfacing seal to prevent reflective cracking was

documented by virtually every district (Figure 5); however, when the cracks were sealed

prior to the overlay, the microsurfaciilg generally had no further problem with cracking.

The perfonnance of the micro surfacing seal itself in effectively sealing the surface of the

roadway was less than satisfactory (Figure 6).

50 • Rated Average = 2.58

w 40 CJ C

~ w 30 0 a:: w a. CJ 20 z ~ a:: 10

0 12345

LOW HIGH-

FIGURE 5: REFLECTIVE CRACKING PERFORMANCE

50 • Rated Average = 2.76

w 40 CJ C ~ Z w 30 0 a:: w a. CJ 20 z i= c a:: 10

0 1 2 3 4 5

LOW HIGH

FIGURE 6: SEALING PERFORMANCE

4

Several districts used microsurfacing to repair potholes. This practice yielded

mixed results. The microsurfacing overlay itself, however, had very few problems with

potholes (Figure 7).

40

w CJ 30 c !Z w u a:

20 w Q.

CJ Z

~ 10 a:

o

• Rated Average = 3.53

1 LOW

2 3 4 5 HIGH

FIGURE 7: POTHOLE RESISTANCE

The general consensus of the survey respondents was that microsurfacing seals

improve ride quality (average rating of 3.74 out of a possible 5), they experience very little

shelling or ravelling (3.6 out of 5), and they are not susceptible to freeze-thaw action (3.74

out of 5).

Materials and EQuipment

Ralumac was used in 32 out of the 34 microsurfacing projects within the last twelve

months. The lack of local source materials was a common complaint in the slurry seal

survey performed last year. This problem seems to have been alleviated. All the aggregate

used for microsurfacing projects within the last twelve months was obtained from local

sources. The most common aggregate used was crushed sandstone. Rhyolite and

limestone were often used, as well.

5

The availability of equipment is still below ideal conditions. The rated average for

this category was 2.9 out of a possible score of 5. The installation of the micro surfacing

seal was agreed to be fairly easy (average rating of 3.7 out of 5).

Overall Perfounance

The overall performance of the microsurfacing seals was very good (Figure 8). An

interesting result of the survey concerns the rated cost effectiveness of the seal. The rated

average of the cost effectiveness for a seal older than 12 months was 4.0 (out of 5) while a

new seal rated only 3.2. Very little maintenance of the slurry seals was documented in the

survey. This might explain the difference between the short-term and long-term cost

effectiveness of the seal. The average cost of micro surfacing was $1.26 per square yard

(with a low of $0.83/S.Y. and a high of $1.74/S.Y.). This is up 15% from last year's

average of $1.07/S.Y.

60 • Rated Average = 4.24

w 50

" III(

!Z 40 w (,) a:

30 w Do.

" z 20

~ a:

10

0 1 2 3 4 5

LOW HIGH

RGURE8: OVERALL PERFORMANCE

6

Case History

There may be some value to reviewing the performance history of the oldest

existing microsurfacing seal in Texas. District 25 has a seal that was 75 months old at the

time of this evaluation. Ralumac was used in a Demonstration Project to correct rutting on

US 287. Since that time, very little maintenance has been required. The ratings for each

applicable category are as follows.

Overall Perfonnance 4

Cost Effectiveness 3

Rutting 3

Sealing 3 Ride Quality 4

Skid Resistance 4

Conclusions

The use of microsurfacing seals has become fairly common in Texas. In the

twelve-month period from November 1989 to October 1990, approximately nine million

dollars were spent on microsurfacing projects. This survey has helped document that

microsurfacing seals will perform very well if they are used in the applications for which

they were intended, but they also perfonn moderately well for a variety of other uses.

D-IO Research would like to thank each district for their cooperation in completing

the survey questionnaires. Many excellent comments and recommendations were received;

a condensed list is included in Appendix B.

7

APPENDIX A

SURVEY QUESTIONNAIRE FORMS

SLURRY SEAL OUESTIONNAIRE

District ___ has not tried slurry seals at this time.

1) What type of seals do you use most often?

2) Do you plan on trying slurry seals in the future?

3) If yes, when and where?

FORM-A

A-1

SLURRY SEAL QUESTIONNAIRE

District: County:

Highway:. ______ _ # oflanes:. _____ _

Cntrl-Sec or Location Description:

Length of Project:

TRAFFIC DATA

AADT: % Truck Traffic:

WEATHER CONDITIONS Ambient Temperature:__ Road Surface Temperature: __

DrylHumid:

Surface condition before application of slurry seal (and/or reason for application):

Work done to surface before application:

Problems with construction and possible solutions:

Are more slurry seal projects planned? H so, when and where?

FORM-B.t

A-2

Is it Ralumac? yes __ Item Number: Material used (tons): Cost ($/sq. yd.): Total seal project cost:

AGGREGATE

Type:

Source:

How long before given to traffic?

I no __

ASPHALT

Type: Grade:

Additives: Source:

Content (%):

Please rate the seal for each relevant category

CATEGORY LOW Overall Performance 1 2 3 Cost Effectiveness 1 2 3 Ease of Installation 1 2 3 Availability of materials/equipment 1 2 3 Rutting 1 2 3 Reflective Cracking 1 2 3 Flushing and Bleeding 1 2 3 Sealing 1 2 3 Ride Quality 1 2 3 Skid Resistance 1 2 3 Potholes 1 2 3 Shelling or Raveling 1 2 3 Freeze-Thaw 1 2 3 Other 1 2 3

HIGH 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 N/A 4 5 NlA

Additional comments or suggestions (special procedures, etc) (use separate page if

necessary).

FORM-B.2

A-3

SLURRY SEAL FOLLOW-UP OUESTIONNAIRE

District: County: Highway:

Cntrl-Sec or Location Description:

Age of Seal (in months):

Describe maintenance activities pertaining to this particular seal:

Please rate the seal for each relevant category

CATEGORY LOW HIGH Overall Performance 1 2 3 4 5 N/A Cost Effectiveness 1 2 3 4 5 N/A Rutting 1 2 3 4 5 N/A Reflective Cracking 1 2 3 4 5 N/A Flushing and Bleeding 1 2 3 4 5 N/A Sealing 1 2 3 4 5 N/A Ride Quality 1 2 3 4 5 N/A Skid Resistance 1 2 3 4 5 N/A Potholes 1 2 3 4 5 N/A Shelling or Raveling 1 2 3 4 5 N/A Freeze-Thaw 1 2 3 4 5 N/A Other 1 2 3 4 5 N/A

Would you use this type of slurry seal again? Please explain.

FORM-C

A-4

APPENDIX B

SURVEY QUESTIONNAIRE COMMENTS

SURVEY COMMENTS

This is a condensed list of the comments given by questionnaire participants. These

comments are representative of some problems encountered in the districts; they do not

constitute official SDHPT guidelines.

1. When rutting is :eresent, place the seal in two courses, one at 18# to 20# per

S.Y. and the second at 15# to 18#. This may prevent the aggregate from

settling and flushing, as it might in a single, thicker layer.

1a. A level-up of ACP should be placed prior to the microsurfacing seal.

2. Use a steel screed instead of a rubber screed; however, this may make the

surface rougher and less attractive.

3. Seal all cracks before applying the microsurfacing seal.

4. Flushed asphalt must have all the volatiles gone before applying the

microsurfacing seal or it will flush through the new seal.

5. This kind of seal is particularly good for areas with high truck traffic.

6. This kind of seal is appropriate for situations where minimal buildup is

desired.

7. To have better control of the percent asphalt in the mix, a half-day check

(minimum) should be required. The specifications governing sampling,

testing, and quality control need to be revised.

8. Do not place too fast A pulled or rippled surface can result.

9. The machine should be stopped as few times as possible. Because the setting

time is low, it is difficult to tie in at joints. When the machine is stopped, the

rear strike off plate should be cleaned to prevent drag·marks.

10. Proper adjustment of the spreader box and a regular, smooth-milled surface are

required for the seal to have good riding surface.

11. Surface preparation should be the responsibility of the contractor.

12. A variable drag box is needed for pavements of irregular widths.

13. A stringline should be used to alleviate alignment and edgeline difficulties.

14. The mix took too long to cure.

15. The stability and Magnesium Sulfate Soundness (MSS) test requirements need

to be revised.1

1 D-9 and the Center for Transportation Research are currently engaged in a study which includes

evaluating current 4 - Cycle MSS requirements for microsurfacing seals.

B-1